Expandable polystyrene type resin particles, which are given expandability, are obtained by impregnating polystyrene type resin particles with a volatile blowing agent such as propane, butane and pentane. The expandable polystyrene type resin particles can be stored at room temperature or in a refrigerated state, because they can retain the blowing agent well. Accordingly, an expanded molded article can be obtained by timely heating the expandable polystyrene type resin particles to obtain pre-expanded particles, and then pouring these into a mold of a molding machine and heating the same. The expanded molded article is widely used as food containers such as fish boxes, shock absorbers for home electric appliances, heat insulation materials for construction materials, and the like as having excellent heat insulating properties, shock-absorbing properties and lightweight properties.
However, expanded molded articles formed from polystyrene type resin have been disadvantageous in that they can be easily charged by friction due to their high electrical insulation properties and therefore attract dust to have poor appearance. In addition, packing materials formed from such expanded molded articles have been disadvantageous in that they cause packed contents to suffer from contamination and electrostatic breakdown by attracted dust.
The pamphlet of WO 2004/090029 (Patent Document 1) discloses a method for obtaining an antistatic styrene type resin expanded molded article. Specifically, styrene-modified olefin type resin particles are impregnated with a volatile blowing agent to obtain expandable resin particles. Thereafter, 100 parts by weight of the expandable styrene type resin particles are impregnated with 0.1 to 2.0 parts by weight of a surfactant to obtain expandable styrene type resin particles having excellent antistatic properties. The antistatic styrene type resin expanded molded article is obtained from these particles.